What happenedA recent study of the family trees of homosexual men concluded that a gene for male homosexuality is passed down through the mothers, sisters, and other female relatives of gay men. The theory, called "sexually antagonistic selection," outlined by the researchers at the University of Padova in Italy, supposes that a gene can hinder reproduction in one gender as long as it boosts reproduction in the other. (PLoS ONE)

What the commentators said This theory explains the "Darwinian paradox of homosexuality," said Andrew Moseman in a Discover magazine blog. Namely, "if being gay is hereditary, and gay people have fewer or no children, homosexuality should have vanished from the gene pool." But since "female relatives of gay men were more fertile than average women," they will keep homosexuality in the gene pool. "Even if the scientists are right, there’s a lot left to be resolved"—homosexuality in females, for starters.

This research "threatens to change our thinking about gay men in several important ways," said William Saletan in Slate. It implies that homosexuality is a trait that can be neither taught nor eradicated. But if male homosexuality is a "side effect of female evolution," how would society treat gay men? Would homosexuality be treated like a genetic mutation? "We medicate sickle-cell anemia," for example, so would we "medicate homosexuality?"

"I don’t disagree that genes influence sexual orientation," said Peter Tatchell in Spiked. But "an influence is not the same as a cause. Genes and hormones may predispose a person to one sexuality rather than another. But that’s all. Predisposition and determination are two different things."